This proposal describes three experiments which will begin the investigation of the ontogeny of sodium ingestion. All three will examine both phenomena of salt ingestion: sodium preference (the voluntary consumption of supra-physiological amounts of salt by salt-replete animals) and sodium appetite (increased sodium intake that results from sodium deficiency). Though these two related but different phenomena have been well-studied, expecially in the rat, virtually nothing is known about their ontogeny or about the contribution of early experience to their adult expression. EXPERIMENT 1 will determine the sodium preference (expressed as a preference-aversion function) of neonatal rats, as well as the age at which the adult-like sodium preference develops. Several concentrations of NaCl will be offered through a benign anterior oral catheter while the pups are isolated from their mothers. In EXPERIMENT 2, neonatal pups will be challenged by adrenalectomy, administration of mineralocorticoid, or a combination treatment of mineralocorticoid and angiotensin II, to discover the exact age of onset of the sodium appetite which is produced in the adult by these challenges. Finally, EXPERIMENT 3 will investigate the effect of early experience with sodium excess and the taste of salt or sodium deficiency on the adult expression of sodium preference and sodium appetite. Both early sodium excess and early sodium deficiency are associated with disruptions in the physiology of body fluid and pressure regulation in rats and in humans; this pilot study will examine the effect of such manipulations on two behavioral components of that regulation. These experimetns have important implications, as the level of salt intake is part of the etiology and therapeutic management of hypertension in many though not all individuals. In particular, the work proposed here may suggest a role for early salt intake in the development of the excessive salt consumption typical in this country.